Central pattern generators are responsible for the generation of rhythmic behaviors such as walking and breathing in both vertebrates and invertebrates. The crustacean stomatogastric nervous system (STNS) has been used as a model system to understand the basic cellular mechanisms and synaptic physiology underlying the generation of motor pattern. The main goal of this project is to characterize the effects of a group of peptides that modulate the motor pattern generated by the stomatogastric nervous system. Given that the system under study is modulated by over 20 substances, it becomes interesting to investigate how similar peptides, yet different in terms of the amino acid sequence, modulate each stomatogastric ganglion (STG) neuron. At the network level, the effects induced by the newly isolated peptide KHKNYLRFamide are similar to those produced by three identified FLRFamide-related peptides. However, we have only partial information of the sensitivity of individual STG neurons to these peptides. The experiments proposed here will provide valuable information about the receptors and conductances activated by these peptides in intact condition and in the absence of modulation, which is a major long-term goal of our laboratory.